Nepal is of roughly trapezoidal shape, 800 kilometres (497 mi) long and 200 kilometres (124 mi) wide, with an area of 147,181 km2 (56,827 sq mi). See List of territories by size for the comparative size of Nepal. It lies between latitudes 26° and 31°N, and longitudes 80° and 89°E.

Nepal is commonly divided into three physiographic areas: Mountain, Hill and Terai. These ecological belts run east-west and are vertically intersected by Nepal\'s major, north to south flowing river systems.

The southern lowland plains or Terai bordering India are part of the northern rim of the Indo-Gangetic plains. They were formed and are fed by three major Himalayan rivers: the Kosi, the Narayani, and the Karnali as well as smaller rivers rising below the permanent snowline. This region has a subtropical to tropical climate. The outermost range of foothills called Shiwalik or Churia Range cresting at 700 to 1,000 metres (2,297 to 3,281 ft) marks the limit of the Gangetic Plain, however broad, low valleys called Inner Tarai (Bhitri Tarai Uptyaka) lie north of these foothills in several places.

The Hill Region (Pahad) abuts the mountains and varies from 800 to 4,000 metres (2,625 to 13,123 ft) in altitude with progression from subtropical climates below 1,200 metres (3,937 ft) to alpine climates above 3,600 metres (11,811 ft). The Mahabharat Range reaching 1,500 to 3,000 metres (4,921 to 9,843 ft) is the southern limit of this region, with subtropical river valleys and \"hills\" alternating to the north of this range. Population density is high in valleys but notably less above 2,000 metres (6,562 ft) and very low above 2,500 metres (8,202 ft) where snow occasionally falls in winter.

The Mountain Region (Parbat), situated in the Great Himalayan Range, makes up the northern part of Nepal. It contains the highest elevations in the world including 8,848 metres (29,029 ft) height Mount Everest (Sagarmatha in Nepali) on the border with China. Seven other of the world\'s eight thousand metre peaks are in Nepal or on its border with China: Lhotse, Makalu, Cho Oyu, Kanchenjunga, Dhaulagiri, Annapurna and Manaslu.

Nepal experiences five seasons: summer, monsoon, autumn, winter and spring. The Himalaya blocks cold winds from Central Asia in the winter and forms the northern limit of the monsoon wind patterns. In a land once thickly forested, deforestation is a major problem in all regions, with resulting erosion and degradation of ecosystems.

Nepal is popular for mountaineering, containing some of the highest and most challenging mountains in the world, including Mount Everest. Technically, the south-east ridge on the Nepali side of the mountain is easier to climb; so, most climbers prefer to trek to Everest through Nepal.

Neotectonics

The collision between the Indian subcontinent and the Eurasian continent, which started in Paleogene time and continues today, produced the Himalaya and the Tibetan Plateau, a spectacular modern example of the effects of plate tectonics. Nepal lies completely within this collision zone, occupying the central sector of the Himalayan arc, nearly one third of the 2,400 km (1,500 mi)-long Himalayas.

The Indian plate continues to move north relative to Asia at the rate of approximately 50 mm (2.0 in) per year.[38] Given the great magnitudes of the blocks of the Earth\'s crust involved, this is remarkably fast, about twice the speed at which human fingernails grow. As the strong Indian continental crust subducts beneath the relatively weak Tibetan crust, it pushes up the Himalayan mountains. This collision zone has accommodated huge amounts of crustal shortening as the rock sequences slide one over another. As such Nepal is prone to frequent earthquakes, a major earthquake happening within every 100 years.[39]

Erosion of the Himalayas is a very important source of sediment, which flows via several great rivers (the Indus to the Indian Ocean, and the Ganges and Brahmaputra river system) to the Bay of Bengal.

Environment

The dramatic differences in elevation found in Nepal result in a variety of biomes, from tropical savannas along the Indian border, to subtropical broadleaf and coniferous forests in the Hill Region, to temperatebroadleaf and coniferous forests on the slopes of the Himalaya, to montane grasslands and shrublands and rock and ice at the highest elevations.

At the lowest elevations is the Terai-Duar savanna and grasslands ecoregion. These form a mosaic with the Himalayan subtropical broadleaf forests, which occur from 500 to 1,000 metres (1,600 to 3,300 ft) and include the Inner Terai Valleys. Himalayan subtropical pine forests occur between 1,000 and 2,000 metres (3,300 and 6,600 ft).

Above these elevations, the biogeography of Nepal is generally divided from east to west by the Gandaki River. Ecoregions to the east tend to receive more precipitation and to be more species-rich. Those to the west are drier with fewer species.

From 1,500 to 3,000 metres (4,900 to 9,800 ft), are temperate broadleaf forests: the eastern and western Himalayan broadleaf forests. From 3,000 to 4,000 metres (9,800 to 13,000 ft) are the eastern and western Himalayan subalpine conifer forests. To 5,500 metres (18,000 ft) are the eastern and western Himalayan alpine shrub and meadows.